On the role of transducin GTPase in the quenching of a phosphodiesterase cascade of vision

• Published in: FEBS letters 1987-11, Vol.224 (1), p.19-22
• Main Authors: Arshavsky, V.Yu, Antoch, M.P., Philippov, P.P.
• Format: Article
• Language: English
• Subjects: 3',5'-Cyclic-GMP Phosphodiesterases - metabolism; 3',5'-cyclic-nucleotide phosphodiesterase; Animals; Biological and medical sciences; Cell physiology; cyclic nucleotide phosphodiesterase; Enzyme Activation; Fundamental and applied biological sciences. Psychology; GTP; GTP Phosphohydrolases - physiology; GTPase; Guanosine Triphosphate - metabolism; Membrane Proteins - physiology; Molecular and cellular biology; PDE; Phosphodiesterase; Phosphoric Monoester Hydrolases - physiology; Phosphorylation; Photic Stimulation; Photoreceptor; Photoreceptor Cells - physiology; Rhodopsin - metabolism; Rhodopsin - radiation effects; Rod Cell Outer Segment - physiology; rod outer segment membranes; rod outer segments; ROS; Transducin; Tα, Tβ, Tγ and Tβγ; Vision, Ocular - physiology; Vision, photoreception; α, β, γ and a complex of β- and γ-subunits of transducin, respectively
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/0014-5793(87)80414-3

The rate of GTP hydrolysis in the active site of transducin and that of the release of the phosphate thus formed have been measured. The former step has been found to be a rate-limiting one. The rate constant for GTP hydrolysis is equal to 0.027 s −1 at 23°C, and 0.07 s −1 at 37°C. Bedsides, it has been shown that the rate of GTPase reaction on the transducin α-subunit does not depend on the concentration of a complex of transducin β- and γ-subunits or on the presence of cGMP phosphodiesterase and a 48 kDa protein from rod outer segments. According to the results, GTP hydrolysis on transducin proceeds too slowly to account for the rapid quenching of a phosphodiesterase cascade in rod outer segments.